A critical consideration in the design of turbojet or turbofan engines for modern aircraft is providing for the need to recover from a variety of engine flameout incidents, including high-altitude incidents relating to compressor stall, temporary fuel system malfunctions (pump power shutdown), and emergency responses to incidents such as engine fire warnings, as well as many lower altitude conditions relating to weather such as excessive water or ice ingestion, etc. Obviously, safety considerations for both commercial and military aircraft requires the ability to recover from these incidents with the least risk to the aircraft, the passengers, and the crew.
Fortunately, current aircraft experiencing incidents of these types have an excellent record of recovery. However, even though successful, the recoveries often involve rapid descents and highly disturbing losses of altitude, situations that are obviously very undesirable. Rapid descents may be intentionally performed after a flameout in order to maintain an adequate engine inlet pressure so as to avoid compressor stall when re-ignition is attempted. Even under favorable conditions, the capability for high altitude re-ignition of a modern turbojet engine that has undergone compressor rotational slowdown using a high energy spark igniter (as is commonly used) is limited to about 10,000 feet altitude with engine inlet Mach numbers below 0.3, and to slightly above 25,000 feet with the aircraft performing a controlled high-speed descent to increase the engine inlet pressure. These are most significant performance disadvantages with important safety implications.
It is therefore an object of the present invention to provide a system which will control the high altitude re-ignition process of an aircraft gas turbine jet engine which has flamed out in such a manner as to avoid compressor stall while reestablishing normal combustor operating conditions.